shut up clang warnings

- Fix some class/struct discrepancies
- Explicit the overloading of `run` in the `Cmd*` classes
- Ignore a warning in the generated lexer

src/libstore/local-store.hh

@@ -296,8 +296,8 @@ private:
 
     void createUser(const std::string & userName, uid_t userId) override;
 
-    friend class DerivationGoal;
-    friend class SubstitutionGoal;
+    friend struct DerivationGoal;
+    friend struct SubstitutionGoal;
 };